Grade II listed mansion Chyknell Hall is set within a 200-acre estate in the Shropshire countryside, and is for sale through Knight Frank estate agents.
Danish businesswoman Corinna zu Wittgenstein-Sayn, aged 57, made headlines over her five-year affair with King Juan Carlos of Spain, between 2004 and 2009, while he was reputedly estranged from his wife, Queen Sofia.
The relationship came to light after a safari to Botswana with the trip sparking a scandal which almost brought down the Spanish monarchy.
The King abdicated two years later.
Ms zu Wittgenstein-Sayn bought the eleven-bedroom property for £5 million in 2015.
She has been involved in a long-running legal action against Juan Carlos, aged 85, who she accused of harassment and of placing her under constant hostile surveillance.
He has denied any wrong-doing and a trial is expected to be heard later this year.
Ms zu Wittgenstein-Sayn, who has a 20-year-old son, Alexander, from her second marriage to the German Prince Casimir zu Wittgenstein-Sayn whom she divorced in 2005, has transformed both the property and gardens since buying the mansion.
It contains a cinema room, neo-classical library and indoor/outdoor kitchen and breakfast room.
Will Matthews, a partner with Knight Frank estate agents, said that the London office was dealing with the sale and that "interest in the property had been shown by prospective purchasers from across the world".